The present invention relates generally to computed tomography (CT) imaging and, more particularly, to a method and apparatus for administering low dose CT scans.
Typically, in computed tomography (CT) imaging systems, an x-ray source emits a fan-shaped beam toward a subject or object, such as a patient or a piece of luggage. The terms xe2x80x9csubjectxe2x80x9d and xe2x80x9cobjectxe2x80x9d shall include anything capable of being imaged. The beam, after being attenuated by the subject, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is typically dependent upon the attenuation of the x-ray beam by the subject. Each detector element of the detector array produces a separate electrical signal indicative of the attenuated beam received by each detector element. The electrical signals are transmitted to a data processing system for analysis which ultimately results in the formation of an image.
Generally, the x-ray source and the detector array are rotated about the gantry within an imaging plane and around the subject. X-ray sources typically include x-ray tubes, which emit the x-ray beam at a focal point. X-ray detectors typically include a collimator for collimating x-ray beams received at the detector, a scintillator for converting x-rays to light energy adjacent the collimator, and photodiodes for receiving the light energy from the adjacent scintillator.
Typically, each scintillator of a scintillator array converts x-rays to light energy. Each scintillator discharges light energy to a photodiode adjacent thereto. Each photodiode detects the light energy and generates a corresponding electrical signal. The outputs of the photodiodes are then transmitted to a data processing system.
Increasingly, there is a need for administering CT scans with reduced radiation exposure to the subject. This need is especially apparent for situations involving patient screening as well as imaging pediatric patients. Exposing a subject to be scanned such as a medical patient to radiation is necessary for acquiring CT imaging data, but limiting the radiation exposure to only that which is needed for acquiring the imaging data remains important especially for those subjects having underdeveloped immune systems such as pediatric patients.
Several techniques have been implemented to reduce radiation exposure to pediatric patients including hardware changes to the types of filters used in the CT system as well as lowering the tube current while acquiring imaging data. Hardware changes to the CT system, however, require a redundancy of imaging stations within a single treatment facility because the CT system designed for acquiring data of pediatric patients has limited applicability for acquiring data of non-pediatric subjects. Further, simply lowering the tube current while acquiring imaging data of the pediatric patient may not be sufficient to reduce the patient""s exposure to unnecessary radiation. Further, simply lowering the tube current while maintaining the same data acquisition trigger frequency may introduce additional noise due to the greater contribution of the data acquisition system (DAS) noise at low signal level.
It would therefore be desirable to design a apparatus and method for acquiring imaging data of a subject with reduced radiation exposure to the subject during acquisition of the imaging data while minimizing the DAS noise impact. Further, it would also be desirable to design such a system that is applicable with known CT systems thereby eliminating the need to make changes to the hardware of the CT system.
The present invention is directed to a method and apparatus for acquiring CT imaging data with reduced radiation dosage overcoming the aforementioned drawbacks. The present invention is particularly applicable for scanning centralized small objects such as a heart or a head as well as acquiring imaging data of pediatric patients. Further, the present invention may also be implemented in patient screening scans where slightly degraded images near the edge of the patient are acceptable.
Therefore, in accordance with one aspect of the present invention, a method prescribing a low dose scan of a subject to be scanned includes the steps of receiving a user input to lower tube current and acquiring a first set of angular views of the subject. The method further includes the steps of interpolating between each view of the first set of angular views and generating a second set of angular views therefrom. The method also includes the step of reconstructing an image of the subject from the first set and the second set of angular views.
In accordance with a further aspect of the present invention, a computer readable storage medium having a computer program stored thereon is also provided. The computer program represents a set of instructions that when executed by a computer causes the computer to reduce the tube current of a CT imaging apparatus used to acquire imaging projections of a subject. The set of instructions further causes the computer to acquire a set of imaging projections corresponding to a set of angular views of the subject. The computer program then causes the computer to determine a set of pseudo-angular views from the set of imaging projections. The set of instructions then cause the computer to combine the set of angular views and the set of pseudo-angular views into a final set of angular views. The computer is then caused to reconstruct an image of the subject from the final set of angular views.
In accordance with yet another aspect of the present invention, a CT system includes a rotatable gantry having an opening therein to receive a subject and a high frequency electromagnetic energy projection source configured to project high frequency electromagnetic energy to the subject. The CT system further includes a detector array configured to detect high frequency electromagnetic energy attenuated by the subject and generate a plurality of electrical signals indicative of the high frequency electromagnetic energy detected. The CT system further includes a computer connected to the detector array and programmed to acquire a set of projections from at least one region of the subject as well as determine a first set of views of the at least one region of the subject from the set of projections. The computer is also programmed to generate a second set of views from the first set of views and reconstruct an image of the at least one region of the subject from the first set and second set of views.
In accordance with yet another aspect of the present invention, a CT system is provided and includes means for acquiring a set of projection data from a set of angular views of a subject as well as means for generating a set of pseudo-angular views from the set of angular views. The CT system further includes a means for forming a final set of angular views from the set of angular views and set of pseudo-angular views as well as a means for reconstructing images of the subject from the final set of angular views.